Impact of continental drift on GPS accuracy

  • Thread starter Thread starter David
  • Start date Start date
Keith Sheppard wrote ...
I was particularly amused by Ricky Gervais' comment to an American audience
at a recent awards ceremony:

"I'm from Britain. You know. We used to run the world before you guys took
over."
Click to expand...

Reminds me of the final words from Sellars & Yeatman's seminal guide to
English history - "1066, and all that":

"America was thus clearly top nation and history came to a."

(It may help any left-ponders to explain that what you call a "period", we
call a "full stop")

David
 
x-no-archive: yes

Karl said:
OK, so are you agreeing or disagreeing with my claim?
Click to expand...

Not every usenet post is a disagreement!

My understanding is that the treaty said something like "we'll draw a
series of lines between points along the 49th parallel as best we can,
and those lines shall be the boundary" and that the boundary is the
imperfect set of lines, not the 49th parallel.

As an interesting aside, I understand that near the Peace Arch border
crossing south of Vancouver, the international boundary is significantly
north of the true position of the 49th parallel.

I read reports several years go of some guys who were going to try to
cross into Canada with some marijuana in their car, but changed their
minds between the border posts.

US customs searched them and found the goods and charged them. They made
the news because the Washington state boundary is apparently defined as
the 49th parallel, not as the US-Canada border, with the result that
whilst they were within the US, they weren't within Washington. Much
legal joy was being had by the lawyers.
 
x-no-archive: yes
Graham W said:
As an interesting aside, I understand that near the Peace Arch border
crossing south of Vancouver, the international boundary is significantly
north of the true position of the 49th parallel.
Click to expand...

About 200m which was the point of my original post. It is not consistent
but generally is it at 49º00'07.n" or 08.n" (WGS84)
I read reports several years go of some guys who were going to try to
cross into Canada with some marijuana in their car, but changed their
minds between the border posts.
Click to expand...

Highly unlikely. That would be like carrying wood into the forest. BC Bud
is of far superior quality to anything he could buy at home. Marijuana is
one of the chief exports from BC to the US.
US customs searched them and found the goods and charged them. They made
the news because the Washington state boundary is apparently defined as
the 49th parallel, not as the US-Canada border, with the result that
whilst they were within the US, they weren't within Washington. Much
legal joy was being had by the lawyers.
Click to expand...

Probably an urban legend as importation of drugs would be under a US
federal law and therefore Washington state bondaries would be irrelevant.
 
[email protected] (Karl Pollak) wrote in
Same as the US-Canadian border on the West Coast is not exactly on the
49th parallel as fixed by a treaty. The error there is about 200m and
can't be blamed on any continental drift.
Click to expand...

The Cananda-USA border does not have any 'error' in it,
because the border is currently defined as a series of
straight lines between border monuments. In some areas
the prior definition was curved lines.
http://www.confluence.org/country.php?id=3#NOTES
 
If you're refering to WGS 84, that's a datum, not a coord system.
Click to expand...

No, that is incorrect. WGS 84 is a coordinate system.

From "NATIONAL IMAGERY AND MAPPING AGENCY TECHNICAL REPORT
8350.2 Third Edition":
The global geocentric reference frame and collection of models
known as the World Geodetic System 1984 (WGS 84) has evolved
significantly since its creation in the mid-1980s. The WGS 84
continues to provide a single, common, accessible 3-dimensional
coordinate system for geospatial data collected from a broad
spectrum of sources.

The WGS 84 Coordinate System is a Conventional Terrestrial Reference
System(CTRS). The definition of this coordinate system follows the
criteria outlined in the International Earth Rotation Service (IERS)
Technical Note 21.

Part of the WGS 84 system is a horizontal datum referred to
as WGS 84. There is also the WGS 84 Geoid, the WGS 84 Reference
Frame, the WGS 84 Gravitational Model, etc. Most people, when
referring to "WGS 84" are actually referring to coordinates
expressed using the WGS 84 horizontal datum.
 
[email protected] (Karl Pollak) wrote in
x-no-archive: yes


About 200m which was the point of my original post. It is not
consistent but generally is it at 49º00'07.n" or 08.n" (WGS84)
Click to expand...

No, that is untrue, as I pointed out in a prior posting:
http://www.confluence.org/country.php?id=3#NOTES

I recall the case, but not enough to find a link on the web,
and I can't recall the specifics, but the defendant's arguments
had to do with jurisdiction and the definition of the location
of the border(s), and they lost the court case.
 
David said:
We all heard of the continental drift phenomenon. I understand the 5
continents are moving a few meters/feet per year. Does the GPS
satelite system have a correction algorithm ? If not, as years go by I
would think that the same GPS coordinate does not locate the same
place on earth.E.g : if my house doorstep is N 50°23.000 E 4°50.000,
after a few years it could have become N 50°23.002 E 4°50.003, because
of continental drift ?

Thanks for your comments.
David.
Click to expand...

Updated periodically

NGA GPS Ephemeris/Station/Antenna Offset Documentation
Effective date November 10, 2004
http://earth-info.nga.mil/GandG/sathtml/gpsdoc2004_11a.html

CORS Coordinates
http://www.ngs.noaa.gov/CORS/metadata1/
 
[email protected] (Karl Pollak) wrote
Click to expand...

It was a pretty weird case, as Karl quite rightly says, why would you
take dope into Canada? I think the answer was that they remembered they
had it in the car when they were approaching the Canadian customs.

As my dim memory stands, part of the problem was they hadn't actually
brought the stuff into the US, so they hadn't committed a federal
offence. It then came down to a question of possession within Washington
state, and their lawyers slightly desparate argument was that they were
between the state line at 49deg N and the international border markers
which are actually north of 49deg N at the Peace Arch, so while they
were in the US they weren't in Washington State.

Dave said:
I recall the case, but not enough to find a link on the web,
and I can't recall the specifics, but the defendant's arguments
had to do with jurisdiction and the definition of the location
of the border(s), and they lost the court case.
Click to expand...

Thanks Dave, I did lots of searching and I was about ready to admit
defeat. I may not be able to find it, but at least I know I'm not going
daft. I am pretty sure we discussed it here or in s.g.s-nav, but google
doesn't turn it up either. I clearly remember forwarding the story to an
Aussie friend who emigrated from Vancouver.

As someone who live in an island nation, Australia, and who has only
ever crossed international borders by road twice in my life, at the
Peace Arch and at Osoyoos, the case took on a special element of bizarre
to me.
 
[email protected] (Karl Pollak) wrote in
x-no-archive: yes


Dave, I am having a discussion on this ng, not on some website. If you
want to discuss something, please do it here.
Click to expand...

I am discussing it here.

In a prior posting in this thread, I pointed out why some
of your assertions about the Canada-USA border were wrong,
and included the above URL as part of that answer.

Rather than repeat myself, in the above reply, I just
included the URL to information that shows that your
assertion is wrong.
 
x-no-archive: yes
Dave Patton said:
Rather than repeat myself, in the above reply, I just
included the URL to information that shows that your
assertion is wrong.
Click to expand...

Just tell me why I am wrong. I'm not about to search some website to find
out what somebody else thinks and hope to prove myself wrong. Pointing to
some website is not a debate Dave.

If you think I say something that is not right, tell me why, don't send me
to some website.
 
x-no-archive: yes

Karl said:
Just tell me why I am wrong. I'm not about to search some website to find
out what somebody else thinks and hope to prove myself wrong. Pointing to
some website is not a debate Dave.
Click to expand...
If you think I say something that is not right, tell me why, don't send me
to some website.
Click to expand...

Karl, he's pointing you to a diagram which shows the relationshiop
between the border markers and 49deg North.

And you are clamping your hands over your ears and shouting:
"I can't hear you!".
 
[email protected] (Karl Pollak) wrote in
x-no-archive: yes


Just tell me why I am wrong. I'm not about to search some website to
find out what somebody else thinks and hope to prove myself wrong.
Pointing to some website is not a debate Dave.

If you think I say something that is not right, tell me why, don't
send me to some website.
Click to expand...

There are lots of reasons people put things on webpages,
including not having to repeat them over and over, and
being able to use images.
If you are unwilling/unable to look at webpages, then
that's your loss.

You said:
"Same as the US-Canadian border on the West Coast is not exactly on
the 49th parallel as fixed by a treaty. The error there is about 200m"

There is no "error", and the border is defined by a series
of straight lines between border monuments, not the 49th parallel.

Someone said:
"As an interesting aside, I understand that near the Peace Arch border
crossing south of Vancouver, the international boundary is significantly
north of the true position of the 49th parallel."

And you replied:
"About 200m which was the point of my original post. It is not consistent
but generally is it at 49º00'07.n" or 08.n" (WGS84)".

The first part of that statement is fairly close, as the border
monuments from 0(Tsawwassen) through 43(which is near Vedder Mountain)
are all north of 49 degrees 00 minutes 07 seconds(NAD83).
It is also true that this is not consistent, but it is not
"generally" at any particular latitude, and in fact the average
location is south of 49 North.
http://www.confluence.org/country.php?id=3#NOTES
 
x-no-archive: yes
Graham W said:
Karl, he's pointing you to a diagram which shows the relationshiop
between the border markers and 49deg North.
Click to expand...
And you are clamping your hands over your ears and shouting:
"I can't hear you!".
Click to expand...

Not at all. He's telling me to go to some website without telling me what I
should expect there.

BTW, you are wrong:
Standard Webster Encyclopedic Dictionary, 48th edition, page 362

:0-)
(get the point?)
 
x-no-archive: yes
Dave Patton said:
You said:
"Same as the US-Canadian border on the West Coast is not exactly on
the 49th parallel as fixed by a treaty. The error there is about 200m"

There is no "error", and the border is defined by a series
of straight lines between border monuments, not the 49th parallel.
Click to expand...

Dave, AFAIK originally the border was defined as the 49th. By people who
had never been out West nor did they particularly give a damn. That is how
it was surveyed. Yes, we have since found out that where they stuck the
sticks in the ground was not exactly the 49th as we define the 49th today.
Being Canadians, good neigbours and realizing the pettiness of the dispute
over a sliver of largely uninhabited territory, we have said "Oh what the
hell, leave the sticks where they are."

Nobody, and I am reasonably sure of this, 100 years ago said "One day, when
we get this Internet thing all set up, there's gonna be a couple of goofs
arguing about this, so let's really screw them up and make the border all
in a wavy line, a bit this way, a bit that way, not enough that anybody
would notice but just enough to mess those two up, besides those straight
lines are so boring, nowattamin?"

If you like, and it makes you sleep better at night, I will amend my
previous statement by replacing the word "error" with the word "difference"
OK? Now you can have a mug of hot chocolate and have a good night's rest
for a change.
Someone said:
"As an interesting aside, I understand that near the Peace Arch border
crossing south of Vancouver, the international boundary is significantly
north of the true position of the 49th parallel."

And you replied:
"About 200m which was the point of my original post. It is not consistent
but generally is it at 49º00'07.n" or 08.n" (WGS84)".

The first part of that statement is fairly close, as the border
monuments from 0(Tsawwassen) through 43(which is near Vedder Mountain)
are all north of 49 degrees 00 minutes 07 seconds(NAD83).
Click to expand...

No, Dave, it is not "fairly close", it is as dead on as cheap GPS will
measure. I can send you the waypoins in Ozi wpt file if you like.

I think it was Graham who mentioned the Peace Arch and that is precisely
what I was referring to in my response to him. It is consistent with the
previous statement I had made about the border being about 200m north of
the 49th parallel.

Other than trying to get another opportunity to promote your website, I
really do not understand what exactly is your nitpicking aim in dragging
this one out.

If the two governments did not start a war over it, I don't know why you
and I are.
It is also true that this is not consistent, but it is not
"generally" at any particular latitude, and in fact the average
Click to expand...

Who the hell cares?
We spoke of the Peace Arch. Feel free to include a few km on either side
of the Peace Arch and my statements are still accurate.
Sheeeesh, some people's kids ...
 
if my house doorstep is N 50°23.000 E 4°50.000,
after a few years it could have become N 50°23.002 E 4°50.003, because
of continental drift ?
Click to expand...

That's how it works. Survey marks around the world are basically
constantly undated to account for continental drift.
 
Not a valid question considering his GPS is at best 3m accuracy and
continental drift is 0.03m per year at best.
Click to expand...

Depends on what type of GPS you're using. Some survey quality GPS
systems have accuracy to 10mm. Very valid in that case.
 

Members online

No members online now.
Total: 44 (members: 3, guests: 41)
Back
Top